Why the hell did Bush send amphibious vehicles to a land-based war?

Rob at Americablog asks this very valid question in the aftermath of Katrina. Amphibious vehicles have lighter armor plating than land-only vehicles, so what on earth is their use in Iraq -- other than fighting war on the cheap?

And how many people are going to YET die in Louisiana and Mississippi because there are not enough amphibious vehicles to deploy in rescue efforts there?

[Edited after calming down to correct title so our resident wingnut troll CRB couldn't continue to feel infinitely superior. Of course he will anyway, but isn't it amazing that he still continues to waste his time with us here? Funny too, isn't it, how he has nothing to say about the demotion of Bunny Green house or Bush's 40% approval rating. Why should he, when it's so much more fun correcting a minor mistake of mine?]